A dhc-8 captain reported aileron trim went uncommanded to full left wing down position. An emergency...

Narrative:

We took off with [first officer] as pilot flying under normal circumstances. No issues until we were climbing through about 6;000 ft. [First officer] said the controls felt like they were heavy in the aileron and we looked and saw that the aileron trim had gone full lwd. We tried pushing the trim switch in the opposite direction but; the trim tab did not move. I pulled out the emergency/abnormal checklist and it directed us to the uncommanded roll checklist. We complied with the checklist. Part of the checklist included transferring aircraft control to the first officer. I took over as pilot flying and we returned to [departure airport]. We declared an emergency and contacted dispatch. No other abnormalities occurred.

Original NASA ASRS Text

Title: A DHC-8 Captain reported aileron trim went uncommanded to full left wing down position. An emergency was declared and a return to departure airport accomplished.

Narrative: We took off with [First Officer] as pilot flying under normal circumstances. No issues until we were climbing through about 6;000 FT. [First Officer] said the controls felt like they were heavy in the aileron and we looked and saw that the aileron trim had gone full LWD. We tried pushing the trim switch in the opposite direction but; the trim tab did not move. I pulled out the emergency/abnormal checklist and it directed us to the uncommanded roll checklist. We complied with the checklist. Part of the checklist included transferring aircraft control to the First Officer. I took over as pilot flying and we returned to [departure airport]. We declared an emergency and contacted dispatch. No other abnormalities occurred.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	937631
Time
Date	201103
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	Dash 8-200
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Component
Aircraft Component	Aileron Trim System
Person 1
Function	Captain Check Pilot
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

A dhc-8 captain reported aileron trim went uncommanded to full left wing down position. An emergency was declared and a return to departure airport accomplished.